Techniques for integrating a metal with a resin is needed in a wide range of fields such as automobiles, consumer electrical products, industrial machinery and parts manufacturing thereof, and many different adhesives have been developed under such circumstances. Included in these are some truly outstanding adhesives. An adhesive that exhibits its function at normal or raised temperature is used to integrally join a metal and a synthetic resin and this method is currently a standard technique.
However, study has been made for a more rational method for joining that does not involve use of an adhesive. An example of a method for joining high-strength engineering plastics to a light metal (such as magnesium, aluminum, or an alloy thereof) or a ferric metal (such as stainless steel) is the method developed by the present inventors, in which a shaped metal is inserted into a metallic mold, a thermoplastic resin is injected into the metallic mold and then the shaped metal and formed thermoplastic resin are integrally joined (hereinafter referred to as “injection joining”). This “injection joining” method was developed through years of research made by the inventors and the details thereof have been disclosed (see Patent Document 1: Japanese Patent Application Laid-Open 2003-251654, for example).
There is another known method in which a special organic compound is used to cover the surface of a shaped metal with an organic phase by organic plating and this is inserted into an metallic mold for injection molding and a thermoplastic resin is injected there to make injection joining (see Patent Document 2: Japanese Patent Application Laid-Open 2000-160392, for example).
In yet another method, an aluminum alloy is oxidized by anodic oxidation, after which it is inserted into a metallic mold and then a thermoplastic resin is joined with the aluminum alloy by hot pressing (see Patent Document 3: WO2004/055248 A1, for example).
When a PBT resin or PPS resin is integrated with an aluminum alloy by the “injection joining” method developed by the inventors, the joint is so strong that breaking this product requires a shear force of 19.6 to 29.4 MPa (200 to 300 kgf/cm2). This “injection joining” method holds promise for use in many different fields such as in manufacturing various devices and various parts. In view of this, the inventors attempted to manufacture a wide variety of parts and products involving integration by the “injection joining” method. As a result, problems were sometimes encountered when the injection joining was performed with a conventional resin molding technique. The thermoplastic resin that is integrated with the shaped metal comes in various shapes, such as a boss or a rib. For instance, when, in a case of a boss with a screw-fastening hole on a base plate, the boss is injection molded using a shaped aluminum alloy inserted in a metallic mold as the base plate, such a problem occurred that the boss always tilts in the direction of a gate mark. If this screw-fastened boss is not provided perpendicularly, problems may occur when it is attached to something. The same problems were encountered with the injection joining of a rib.
The problems arising when injection joining is performed with prior art will be described more concretely with reference to FIGS. 17 and 18.
FIG. 17 is an oblique view of a composite 100 in which a shaped thermoplastic resin having a boss, a seat, etc. is joined by injection joining to an aluminum alloy piece (shaped metal) 20. FIG. 18 is a front view of the composite 100, and is a diagram schematically illustrating the error that occurs in the perpendicular precision of a boss 101.
A commercially available A5052 aluminum alloy sheet with a thickness of 1 mm was purchased and cut into rectangular pieces with a dimension of 40 mm×60 mm. A dipping jig completely covered with vinyl chloride resin was fabricated by braiding stainless steel wire and dipping it into molten vinyl chloride resin and then many of the above-mentioned aluminum alloy pieces were fitted therein.
A 15% aqueous solution of a commercially available aluminum degreaser was placed in a degreasing tank and brought to 70° C. The dipping jig with the aluminum alloy pieces therein was dipped for 5 minutes in this tank and then washed by dipping it in a water rinsing tank. This product was then dipped for 1 minute in a 40° C. preliminary acid washing tank containing a 1% hydrochloric acid aqueous solution, and then washed by dipping it in another water rinsing tank.
This product was then dipped for 1 minute in a 40° C. alkali etching tank containing a 1% caustic soda aqueous solution, and then washed by dipping it in another water rinsing tank. Next, it was dipped for 1 minute in a 40° C. neutralization tank containing a 1% hydrochloric acid aqueous solution, and then washed by dipping it in another water rinsing tank. After this, it was dipped for 1 minute in a 60° C. main treatment tank containing a hydrazine monohydrate aqueous solution with a concentration of 4%, and then washed by dipping it in another water rinsing tank. The aluminum alloy pieces, still fitted in the dipping jig, were placed in a warm air dryer, dried for 15 minutes at 40° C. and 5 minutes at 60° C., thereafter were removed from the dipping jig, wrapped in aluminum foil and stored.
A metallic mold was fabricated for molding the composite 100 shown in FIG. 17 by injection joining. An aluminum alloy piece 20 that had undergone the above-mentioned dipping, washing and other such pretreatment was inserted into the mold, which had been heated to 140° C., and a PPS resin (polyphenylene sulfide resin; trademark SGX120, made by Tosoh Co.) was joined by injection joining by a method in which the resin was injected from an injection gate 105 at an injection temperature of 310° C. Approximately twenty of the composites 100 were injection molded. The PPS resin flowed into and filled a boss (upright molding) portion 101 via a runner 103 and a seat 102, where a hole 104 had been formed in the boss 101. The integrated composite 100 was placed for 1 hour in a air dryer which was set at 170° C. and then gradually cooled to relieve internal strain.
When we look closely at the boss 101 of the composite 100 here, we see that the upper part is tilted toward the mark of injection gate 105. The amount of tilt was measured with a three-dimensional gauge. Specifically, using the center position at the bottom of the boss as a reference, the error of the center position at the top of the boss was measured. This error δ was from +0.20 mm to +0.27 mm. The height h of the boss 101 was 15 mm. If we express this using the direction on the injection gate 105 mark side as the positive direction with respect to the boss 101 center, the boss 101 was tilted to the injection gate side by (+0.20 mm to +0.27 mm)/15 mm (see FIG. 18).
In the field of injection molding technology, there is a known technique for increasing the perpendicular precision of the molded part (see Patent Document 4: Japanese Patent Application Laid-Open H07-156195, for example) in the molding of parts with a large height such as a boss. This technique relates to outsert molding, that is, molding and integrating in such a manner that the bottom of a resin boss sandwiches a holed substrate, where restricting means are provided for restricting the flow and the orientation of the resin material, which improves the perpendicular precision of a part with a large height such as a boss. However, while this method might be favorable for outsert molding, it was not suited to the injection joining discussed in Patent Document 1. Specifically, in the above-mentioned “injection joining” method, the high-temperature and high-pressure resin flow needs to come into contact with a metal surface in which there are minute recesses, which precludes the use of a method in which the resin material flow, etc., is restricted by a restricting means as with the technique of Patent Document 4. In other words, the high joint strength obtained with the “injection joining” method of Patent Document 1 could not be obtained with the technique of Patent Document 4, and so the molding and integration were made in such a manner that the substrate was sandwiched by the resin. Also, when integration was achieved by outsert molding by the technique of Patent Document 4, the perpendicular precision of the part with respect to the substrate was still not adequate.
Specifically, in a method in which a thermoplastic resin is brought into contact with a metal surface without the strength of its flow being diminished and a shaped thermoplastic resin having a boss, rib or other such upright molding is integrated by injection joining to a shaped metal, there has been no technique with which the perpendicular precision of the upright molding with respect to the shaped metal could be kept within the desired range, hence there has been an urgent need for such a technique to be developed.
The inventors have put diligent efforts over many years for developing, disseminating, etc, a technique for integrating a shaped metal and a shaped thermoplastic resin by the above-mentioned “injection joining” method. The present invention was conceived in light of resolving those problems encountered with the above-mentioned “injection joining” method and achieving the following object.